JPH0151521B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the production of sintered particulate structures and their final compression forming, and more particularly to the production and subsequent processing of inelastically compressible ductile particulate material structures.

Precision parts according to the prior art are generally formed by machining from forged metal, or by casting and then machining the metal, or by solidifying particulate material and then processing it according to well-known powder metallurgy techniques. Ru. Forgings and parts formed by forging are substantially incompressible due to the incompressible nature of the starting materials.
Conventional powder metallurgy metal parts are also substantially incompressible. First, a molten metal, such as copper, is injected into a porous particulate material to increase the ductility of the foam but reduce the pores, making the part incompressible. shall be. In a fired foam that has only been sintered, the constituent materials are brittle and non-ductile; compressing the fired foam results in cracking, similar to crushing cast iron. Thus, incompressible prior art materials cannot be further compressed, and parts that are considered compressible are actually incompressible and lack ductility so that their shape does not change. For the above-mentioned reasons, compression molding using a closed die has not been possible in the past. This is because some materials cannot be compressed, and materials with zero or little ductility cannot hold their shape when compressed. For this reason, metal compression molding has not conventionally been used to manufacture high-precision parts, especially parts that require high precision.

SUMMARY OF THE INVENTION Accordingly, the object of the present invention is to provide a method for the production and subsequent processing of inelastic, compressible, ductile granular material structures, which allow the fabrication of precision parts by compression molding of metals.

The present invention can be summarized as follows. Ductility is controlled by controlling the particle size and/or the sphericity of the particles of the granular material; the smaller and spherical the particles are; The more ductile the material becomes. In order for such materials to have compressive properties, it is desirable that the pores have a gas-tight shape with a controlled pore volume to feedstock volume. The particulate material itself must have properties that allow it to be ductile. The total pore volume of the sintered body and the volume ratio of the sintered material are controlled by the particle size, the firing process, the properties of the material, and the initial formulation before firing (i.e., the volume ratio of the binder to the granular material). However, the range is from 1% to 25%, preferably from 4% to 8%.
According to the present invention, even a material that does not exhibit ductility per se can be made into a material that has ductile and/or compressible properties, and is then formed into a predetermined shape, the binder is removed, and the desired shape is formed. Fired according to conventional methods, except that the firing process is controlled (as needed) to control porosity.

The materials mentioned above are shaped by inelastic techniques as the particles are compressible due to the voids and the compressed material retains its compressed shape. The above molding is
This is done using well-known coining technology. Precision parts having densities close to the theoretical maximum density of the contained materials can be fabricated using such techniques. According to the method of the present invention, a part is formed and fired to dimensions that are substantially the same or only slightly larger than the desired final shape. This part is then placed inside a die and compression molded. Conventional substances (materials)
It is compressed into the shape of the die very precisely. Of course, the degree of compression volume in the molding machine needs to be equal to or less than the volume of the pores in the material being molded. In this way, the atomizer part can be molded to predetermined precise dimensions substantially free of burrs.

The present invention provides a plastically compressible, permanently deformable raw material that is finished compression molded into a precision part that exactly replicates the mold cavity and exhibits high ductility. The degree of compression and ductility is controlled and predetermined. The above-mentioned raw materials are prepared by preparing particulate material and a binder and mixing them according to conventional techniques. The ductility of the material and the final volume ratio of pores after firing of the molded body are determined by the time and temperature during the firing process,
It is determined by the particle diameter of the granular object, the sphericity of the particles, the chemical characteristics of the particles, the firing atmosphere, etc.
The diffusion of material from particle to particle must be comparable to the particle size, and it is desirable to minimize the range of particle size variation. This can be easily determined for each material with simple experimentation to obtain the desired porosity and ductility of the final product before firing. The obtained fired product exhibits a predetermined ductility and can be compressed by a predetermined amount, so this fired product can be subjected to final compression molding by coining.

In order to manufacture precision parts using the above-mentioned raw materials, first a preform (a shape before final compression molding) is made as described above. This brifome is substantially similar in shape to the final product except that its volume is greater than that of the final product. Note that the difference in volume between the preform and the final product is less than or equal to the volume of the pores in the preform. The preform is then placed into a compression molding device (eg, a coining device) and compression molded within the die of the coining device. The preform is precisely compressed into the shape of the die with adequate bounce allowance. Because the compressed volume of the preform exactly matches the volume of the die, there are no burrs and the density of the precision part is very close to the maximum density of the material of the precision part.

A member with no pores is difficult to form by coining using a closed die, and if formed forcibly, part of the material will be pushed out from the dividing surface of the die, resulting in burrs.
A member with a porosity suitable for coining using a closed die can also be obtained by known powder metallurgy methods.
Most of the pores in the member (sintered body) are continuous pores and do not become independent pores even by coining.
Therefore, the compression molded product obtained by coining is also breathable. Many precision parts of chemical equipment, electronic equipment, medical equipment, etc. must be impervious to gas leakage and contamination. If a sintered body in which substantially all the pores are airtight closed pores is compressed by coining according to the method of the present invention, an air-impermeable precision part can be obtained at low cost. The ratio of the total pore volume of the sintered body to the volume of the sintered material is 4 as described above.
% to 8% by coining (approximately 1 to 8% for each dimension)
3% compression rate) can be achieved (this also applies to sintered bodies with air permeable pores).
If the sintered body has an extremely thin wall (approximately 20 μm or less), some of the pores may be non-airtight and may exhibit some air permeability even after finishing by coining.
If the diameter is 75 μm or more, literally all the pores become airtight independent pores, and a part that shows no air permeability even in a leak test using helium gas can be obtained.

Next, embodiments of the present invention will be described in detail. First, a particulate material and a binder are mixed to form an inelastic, compressible raw material (ie, a raw material that retains a reduced volume when compressed and deformed). The particulate material can be any material that can be granulated and has potentially ductile properties (ie, the particulate material can be later converted from a brittle material to a ductile or malleable material). The interparticle diffusion coefficient of the particulate material must be large enough to allow firing at a suitable rate. The term "suitable" as mentioned above is based on the economics of the granules produced. Materials that meet this requirement are iron, steel, almost all ductile metals, and ductile alloys.

The particle size of particulate matter particles varies depending on conditions.
The preferred particle size is usually 1 to 5 microns, but for other specific materials it may be several tenths of a micron or more than 10 microns. Tungsten particles are usually a few tenths of a micrometer in size. The lower limit of the particle size depends on the flowability of the mixture of doinda and particulate material, and if flowability exists, the particle size is preferably as small as possible. The minimum particle size of the flowing particles is a function of the interfacial energy between the binder and the surface of the particulate material particles.

Theoretically, it is desirable that the granular material particles have a spherical shape. That is, it is desirable that the particles have a shape that minimizes the total surface area of the particles per unit volume of the particles. Therefore, the ideal shape is spherical, although oval and other similar shapes are acceptable.
Although dendritic and protruding shapes may produce good results in some cases, they are undesirable.

The binder is chemically inert to the particulate material and has a plasticity that allows it to be easily removed after the part has been formed into the desired shape prior to firing, such as polyethylene, nylon, polypropylene, Carnaupawax, and beeswax. etc. Many waxes, paraffins and other caking substances are required.

The amount of binder relative to the amount of granular material is sufficient to completely fill the voids between particles of the granular material.
The maximum ratio of the amount of particulate material to the binder used is desirably determined with consideration to obtaining the flow conditions necessary for molding. Next, if it is desired to adjust the pore volume of the final fired product, consideration should be given to using less than the maximum amount of particulate material inside the binder.

Stir the binder and particulate matter evenly,
The homogeneous mixture is then formed into molded articles by conventional techniques well known to those skilled in the art, such as injection molding, extrusion, casting, etc. After molding, U.S. Patent No.
The binder is removed using the techniques disclosed in British Patent Nos. 2,939,199, GB 779,242 and GB 1,516,079, or other suitable techniques now existing and emerging in the future. The molded article, from which the binder has been removed, is then fired essentially according to conventional techniques, except that the pore size within the molded article is controlled and adjusted during the firing process, as explained below. Since the porosity is controlled, the void volume ratio with respect to the volume of the fired product can be controlled.

The final fired product has high ductility and compressibility properties, with voids or pores evenly distributed throughout the material. The above-mentioned material after firing is finished and compression molded into a desired shape, making it possible to obtain a very precise and very inexpensive shaped product compared to conventional methods. In the case of coining, the fired (sintered) molded product has substantially the same shape as the product after coining. However, the fired product has a slightly larger volume than the final product, and this difference in volume is approximately equal to or less than the volume of the voids or pores in the fired product. During compression in the coining process, the material must flow without overflowing from the mold cavity, so if the pore volume inside the material is equal to or greater than the volume difference between the fired product and the final product, For example, all of the material in the coining remains within the mold cavity, reducing the possibility of flash formation. Additionally, the density of the final molded product is substantially equal to or very close to that of the unporous raw material, so that the coined or finished compression molded material in the mold has a density of 0.01 mm (a few thousandths of an inch). ) or better. This is a coining system for fired products,
In particular, this is achieved by placing it in the mold cavity,
First, coining is started as usual, and the fired product is compressed into the shape of the mold, as described above. The molded article is then removed from the mold, free of flash and having a shape that substantially conforms to the shape of the mold. Coining occurs at temperatures in the region where the sintered material is ductile.

Example Average particle size 4-7 microns and specific surface area 0.34 m ² /
315 g of substantially spherical nickel granular material (Inco Type 123 nickel powder) was mixed with 35.2 g of carnauba wax. This mixture was placed in a 1 quart laboratory type sigma blade mixer and mixed for 1.5 hours at 100°C. material,
A homogeneous, moderately viscous plastisol was obtained. It was taken out from the mixer and left to cool for 1 hour until the carnauba wax solidified. The solidified material was crushed with a hammer and the crushed material was placed in a 0.44 (1.5 oz) capacity injection molding machine. Several dozen rings were formed in an injection molding machine. Three rings were randomly removed and placed on laboratory filter paper in a BlueM laboratory oven, and the temperature was gradually increased from ambient temperature to the melting point of the carnauba rock binder over a period of 20 minutes. The oven was left at this temperature overnight for about 12 hours, after which the rings of carnauba wax on the paper were observed. Then the temperature was increased to 100℃ for 8 hours.
and kept the oven at this temperature overnight. The next day, the wax ring formed on the filter paper had increased significantly. The oven temperature was increased to 150°C for 48 hours and then to 200°C for 8 hours.
Let the oven cool and when the temperature is close to room temperature,
He took out three rings. This ring was placed in a kiln with a controlled atmosphere. The atmosphere was maintained at 90% argon and 10% hydrogen, with a dew point of -60°C.
It was below. Furthermore, during the next 24 hours the temperature was raised from ambient to 371.1°C (700°) and held there, then linearly increased to 1176.7°C (2150°) over an additional 6 hours.
〓). After holding this temperature for one hour, the kiln was closed and allowed to cool to substantially room temperature. The two rings were removed from the kiln, weighed and placed in a pycnometer. The density of each ring was 8.54 g/cc. A section for examining the metallographic structure was prepared from one sample, buried in Bakelite, polished, and etched. These operations were performed in accordance with ASTM regulations. The sections were then observed under a microscope. It was found that the spherical pores became substantially homogeneously distributed throughout the sample. The pores were much smaller than the crystal diameter and tended to lie along the crystal interface. The general appearance was the same as that of a forging with spherical pores. The second ring removed from the kiln was measured and its diameter ranged from 0.890 inches to 2.25 cm.
(0.886 inch), and a perfect circle could not be obtained. Second ring then diameter
It was placed in a 2.250 cm (0.885 inch) circular die and pressed through the die with an arbor press at room temperature. The ring was measured and found to have a substantially uniform diameter of 2.250 cm (0.886 inch). The part of the ring pressed through the die was shiny in appearance. After checking the weight, the density measured in a pycnometer was 8.65. The weight of the parts remained substantially constant. A metallographic section was also prepared for the second ring using the above method. Because the outer circumference of the ring was compressed, the uniform spherical pore structure was deformed, and the pores in the outermost layer were compressed into an oblate shape, whose long axis was the same as the diameter of the sphere, and whose short axis expanded along the radial plane of the ring. was. The spherical pores present along the inner diameter of the ring remained relatively unchanged.

EXAMPLE The example was repeated using the same equipment, but
The particulate material was changed from nickel to substantially spherical iron with an average particle size of 4-6 microns. In this example,
278.19g of iron was mixed with carnauba wax.
Tests similar to those in the Example were conducted with substantially the same results except that the density of the ring removed from the kiln was approximately 7.46. The same results as in the example were obtained when the ring in the die was compressed at room temperature in an arbor press.

EXAMPLE The same procedure as described in the example was repeated except that a mixture of nickel and iron was used instead of nickel alone. 50% by weight of nickel as described in the example and iron as described in the example.
50% by weight was used and this was mixed with 35.2g of carnauba wax. The results were the same as described in connection with the examples. Although the density of the ring after removal from the kiln was not specifically measured, the volume after removal from the die was reduced. The weight of the fired body after firing and after removal from the die was substantially the same. Metallographic microscopic observation of the product revealed that the nickel and iron were not separated, but rather a true alloy.

Example A thermoplastic binder was added to a mixture of 2% by weight of nickel powder consisting of approximately spherical particles with a particle size of 3 to 4 microns and 98% by weight of iron powder consisting of approximately spherical particles with a particle size of 4 to 5 microns. The mixture was molded into a disk shape by injection molding. The binder was removed from the molded body in the same manner as in the examples and then sintered.
The sintered disk has a diameter of 15 mm, a thickness of 1 mm, and an apparent density of
It was 7.73 g/cm ³ and about 98% of the degree of vacuum (7.89 g/cm ³ ) (porosity 2%). Sintering caused nickel and iron to interdiffusion and form an alloy. As a result of a test using helium gas, this sintered body was found to be non-porous. This sintered body was compressed by coining at room temperature to a thickness of 0.99 mm. During coining, almost no springback was observed. After that, the test using helium gas was repeated, and it was still non-permeable.

Comparative Example A 2% Ni-98% Fe alloy powder having a particle size of about 150 microns was press-molded into a disk shape, and the compact was sintered. The sintered disk has a diameter of 15 mm, a thickness of 1 mm, and a density of 6.9 g/cm ³ .
The porosity was 13.5%. As a result of testing with helium gas, this sintered body was found to be extremely breathable. This sintered body is compressed by coining at room temperature to reduce its thickness.
It was set to 0.99mm. There was some springback when coining. After that, the test using helium gas was repeated, and it was found to be as breathable as before coining.

Although the invention has been described in connection with specific preferred embodiments, it will be obvious to those skilled in the art that many changes and modifications may be made and the invention is therefore limited to only those embodiments. Needless to say, this is not something that can be done.

Claims (1)

[Scope of Claims] 1. A method for producing a sintered particle structure and compressing the sintered particle structure to obtain a desired shape and size, the method comprising: producing a granule consisting of a predetermined amount of sinterable near-spherical particles; (1) mixing a substance and a binder to coat substantially the entire surface of the particles of the granular material with the binder;
a step (2) of molding the mixture obtained in step (1) into a structure of a desired shape; a step (3) of removing the binder from the structure obtained in step (2); The particle structure after the binder has been removed in step 3) is fired by controlling time and temperature to ensure that substantially all the pores are airtight closed pores and the ratio of the total pore volume to the volume of the sintered material is a predetermined value. (4) obtaining an inelastically compressible sintered body with a value of A method comprising a step (5) of precisely finishing the sintered body into a desired shape and size. 2. The method of claim 1, wherein the particulate material is selected from ductile metals, ductile alloys, and non-ductile materials that become ductile after firing. 3. The method according to claim 1 or 2, wherein the particle size of the fine particles is 10 microns or less. 4. The method according to any one of claims 1 to 3, wherein the binder is wax.